In the non-ferrous metals industry, scrap recycling has become a way of economic life. In fact, long before environmental concerns and conservation began to drive scrap recycling efforts, recycling of aluminum, copper, zinc, lead and tin has occupied a firm nitch in the marketplace.
In the aluminum recycling industry in particular, refining processes are complicated greatly by the potency of aluminum to oxidize quite readily. Consequently, refining by oxidating reactions alone, common for other non-ferrous metals, is not feasible. Similarly, aluminum has exceptionally strong alloying characteristics with a variety of other metals, therefore, a broad range of metallic impurities must often be removed during processing. Along these lines, the removal of magnesium has become a particular focus within the industry. The ability to remove magnesium from molten aluminum is made possible by a favorable chemical reaction between manganese and chlorine as described herein below.
Although the molten aluminum must be treated, the ultimate goal in the aluminum cast house is to maintain and/or continuously improve product quality while pushing the production rate upward. Some of the key factors which are monitored to meet product quality requirements include metallurgical composition (alkali impurities), inclusion levels, and gas content.
In the production scheme, the charging process occurring in the melting furnace, takes up a large majority of the overall time. The focus of this invention is to provide an improved gas injection pump that allows a decrease the overall production time. Gas injection pumps of the type depicted in U.S. Pat. Nos. 4,052,199 and 4,169,584, herein incorporated by reference, are the focus of this invention. In fact, the gas injection pumps described in these patents are significantly improved by the use of the present inventive discharge outlet.
As generally outlined above, the secondary production of aluminum alloys often requires the use of a reactive gas to lower magnesium content and/or an inert gas to remove inclusions and hydrogen. Moreover, in order to achieve a desired final magnesium specification for the materials being processed, magnesium removal must occur during the melt refining process. In many operations today, gas injection pumps are considered the most effective tool for this task.
Typically, chlorine is utilized in the treatment of molten aluminum containing undesirable magnesium levels. More particularly, degassing of the molten aluminum with chlorine has the following result: ##EQU1##
As can be seen, the reaction of the molten aluminum with chlorine ultimately results in the formation of magnesium chloride which collects as a dross on the surface of the molten aluminum in the furnace and can be skimmed away.
Generally, those skilled in the art determine the effectiveness of reactivity by assessing the amount of chlorine which can be introduced into the molten aluminum per unit time. In this context, the maximum amount of chlorine solubilized in the molten aluminum per unit time is readily determinable because aluminum chloride gas which is not reactively scavenged by the magnesium evolves to the surface and decomposes to hydrogen chloride which is visible as a white vapor when in contact with moist air. Under extremely poor reaction conditions, chlorine itself may not be scavenged by the aluminum and can also be directly emitted from the bath. Given the potential for environmental damage and the hazardous nature of chlorine and hydrogen chloride gases, such results are highly undesirable.
Accordingly, commercial gas injection pumps are operated at a level to prevent such emissions. Prior to the present invention, the primary mechanism for increasing the quantity of chlorine reacted and the corresponding rate at which the magnesium level is reduced, was to operate the pump at higher speeds. Of course, this proves very stressful on the dynamic components of the pump.